The present invention generally relates to flyer plates and, more specifically, to laser initiated flyer plates having multiple layers of material.
Flyer plates have been used for detonating explosives since their invention in the late 1960's. Originally, these flyer plates were electrically operated, utilizing an electrically produced plasma to accelerate the plate. It was subsequently discovered, after development of the laser, that laser induced plasmas could be used for plate acceleration.
Current laser initiated explosives or energetic materials operate by either of two methods: thermal runaway, or exploding a metal film to generate a high temperature in a manner similar to an exploding bridgewire. The first of these, thermal runaway, is a slow process requiring a period ranging from several hundred microseconds to several milliseconds to attain plate acceleration. Additionally, thermal runaway requires the addition of undesirable additives to the energetic material in order to reduce energy and thermal requirements to a practical level.
The second, the exploding metal film, is effective for detonation of low density (.apprxeq.0.5 Theoretical Maximum Density-TMD) secondary explosives, but is not effective to produce detonation at reasonable energies for high density (=.apprxeq.0.9 TMD) explosives.
There is currently significant interest in inertial confinement fusion, where large amounts of energy are directed at a sphere of fuel. Although laser beams are now being used in testing, it is conceivable that multiple flyer plates could be launched at the fuel sphere, or that an imploding flyer plate could be on the fuel sphere. The flyer plate may reduce or eliminate the pre-heat problem with large, high power lasers. The invention also finds application in one-dimensional impact of metals or other materials used in shock physics and high strain rate materials research.
The basic prior process for accelerating foils by laser beams involves focusing a laser beam on a free-standing foil in order to convert a portion of the thickness of the foil into a plasma. This plasma will drive a segment of the foil toward a target. Conventional laser interaction with metals produces penetration of the laser beam into the metal of only a few hundred angstroms. The energy deposited in the metal by the laser results in formation of a plasma within a few ns, which plasma drives a flyer plate toward a target.
This process, although effective in settings where laser, focusing lens and free standing foil can all be located in reasonably close proximity is not amenable to use in harsh environments, where equipment such as lasers would not be suitable. It is also not suitable for all geometries, as when sufficient access to the foil is not possible. Additionally, when the laser is used in outside or unsecured applications, it is susceptible to damage and perhaps even false initiation. These problems were overcome by the previous invention which is disclosed in U.S. Pat. No. 5,029,528, issued Jul. 9, 1991, entitled Fiber Optic Mounted Laser Driven Flyer Plates. This patent teaches the launching of flyer plates directly from the end of optical fibers. This allows the plate to be launched from positions inaccessible to and remote from the laser light source.
These prior laser initiated flyer plate systems were based primarily on either a single layer of metal, or multiple layers of metal, dielectric, and metal, on a substrate or optical fiber end. While all are effective, there are significant differences in plate velocity and kinetic energy.
The present invention improves upon these prior flyer plate systems by the introduction of a layer of carbon between the substrate or fiber optic end and the flyer plate. This layer of carbon provides several benefits which allow the launched plates to attain higher terminal velocities than was achieved with the prior art.
It is therefore an object of the present invention to provide laser initiated flyer plates which are capable of attaining high terminal velocities.
It is another object of the present invention to provide laser initiated flyer plates in which the pressure of the driving plasma is equalized across the spatial extent of the flyer plate, creating a flatter plate.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.